Hi,
It is not possible to achieve the kind of shipping you want natively via Shopify. You will need to use a shipping rate app like ShipMagic to do so.
Please note that you need CCS enabled on your store to use any shipping rate app from the Shopify App Store.
The app is not workable in Basic plan as it require CCS feature enable which is only possible on Shopify or Advance plan which is costly compare to other apps.
When it comes to Shopify flat rates, it’s important to note that you cannot determine shipping costs solely based on the unit cost.
However, you do have the option to establish various weight ranges and set up corresponding shipping rates. In your specific situation, you can set the shipping cost at $200 instead of the current $10. To do this, you may need to configure different weight slabs such as 20-30, 30-40, and so on.
It’s worth mentioning that you’re currently receiving the same rates for shipments weighing 100Kg because you haven’t configured a maximum weight limit.
If these options don’t meet your requirements, you might consider enabling CCS and utilizing an app to achieve the desired unit cost per weight.